U.S. Pat. No. 3,639,278 to Hwa, issued Feb. 1, 1972, relates to compositions for inhibiting and removing calcium and magnesium scales (e.g. carbonate, phosphate, sulfate and hydroxide scales) from heat transfer surfaces such as cooling water systems, cooling tower systems, industrial evaporators and boilers. (Hwa says that "because of their inverse solubility, these compounds [scales] tend to precipitate onto heat-exchange surfaces", see Col. 1, lines 32-34). These compositions comprise glycolic acid, and optionally but preferably, lignosulfonic acid or its respective water-soluble salt. See also U.S. Pat. No. 3,639,279 to Gardner et al, issued Feb. 1, 1972, which discloses removal of scale from subsurface and surface equipment used with oil and gas wells by an aqueous basic solution of diglycolic acid salts, salts of substituted acids of a diamine or tertiary amine such as EDTA, and a base such as ammonium, sodium or potassium hydroxide.
U.S. Pat. No. 4,357,254 to Kapiloff et al, issued Nov. 2, 1982, relates to a composition for cleaning fouled reverse osmosis membranes used in water purification systems. These membranes can become fouled with calcium and magnesium scales, as well as iron scales and organic fouling materials. The composition used to clean these membranes comprises a combination of monobasic sodium phosphate, dibasic sodium phosphate, citric acid, malic acid and a nonionic surfactant. Kapiloff et al specifically teach that malic and citric acid serve the dual function of dissolving calcium and magnesium scale, while preventing precipitation of phosphates caused by iron. See also U.S. Pat. No. 4,496,470 to Kapiloff et al, issued Jan. 29, 1985, discloses a similar cleaning composition based on monobasic sodium phosphate, dibasic sodium phosphate, at least one of citric, malic and sulfamic acid, and a nonionic detergent.
U.S. Pat. No. 4,452,703 to Ralston et al, issued June 5, 1984, relates to a method for preventing the formation of scale in sugar juice evaporation equipment. This is achieved by adding the sugar juice from 0.1 to 200 ppm of a polycarboxylic acid (or its salt) selected from polymaleic acid, amine adducts of maleic anhydride polymers, phosphonobutanetricarboxylic acid, phosphinocarboxylic acids and copolymers of acrylic acid and an hydroxylated lower alkyl acrylate.
U.S. Pat. No. 3,622,379 to Fehmerling, issued Nov. 23, 1971, relates to a method for treating shells from marine creates to remove material capable of sustaining microorganism growth and to produce a shiny natural appearing surface. In this method, the shells are contacted with an aqueous solution of 0.05 to 2.5% by weight of an acid capable of forming a substantially insoluble calcium salt upon the surface of the shell. These acids include phosphoric, citric, tartaric, malic, lactic, fluoric or fumaric acid. This acid solution is maintained at a temperature between 175.degree. F. (79.4.degree. C.) and 212.degree. F. (100.degree. C.) to react the acid with the calcium present in the shell so as to form a coating of insoluble calcium salt on the surface of the shell. The shell is then subjected to alkaline treatment with a solution of an alkaline salt, such as sodium carbonate or sodium bicarbonate, at a temperature between 175.degree. F. (79.4.degree. C.) and 212.degree. F. (100.degree. C.) to produce a relatively insoluble protective coating which is substantially impervious and continuous on the shell.